1. Field of the Invention
The present invention relates generally to wet chemical analyzers, and more particularly to an analyzer used for monitoring hydrogen sulfide in waste water.
2. Description of the Related Art
Hydrogen sulfide (H.sub.2 S) is a gas released as a by-product of biological activity in the collection and treatment of waste water. H.sub.2 S is extremely corrosive to equipment and poisonous to the human body. In addition, the majority of odor complaints incurred by waste treatment operations can be traced to fugitive emissions of H.sub.2 S.
H.sub.2 S gas is soluble in water. However, if water containing dissolved H.sub.2 S is agitated, the H.sub.2 S tends to come out of solution as a gas. This gas is corrosive and poisonous. Several control strategies are employed in the industry to control the emission of H.sub.2 S gas. It is common practice to mount free air H.sub.2 S detectors just above flowing streams of waste water at points of agitation. These include weirs, flumes, inverts, pump stations, etc. These free air sensors detect the H.sub.2 S only after it is released into the air. Because they are affected by air currents, they do not give any reliable data about the concentration of H.sub.2 S in the stream being monitored. Essentially these devices become air quality violation yes/no indicators. They indicate either that there is a violation or that there is no violation. The most efficient way to control H.sub.2 S is to convert it into inert compounds while it is still dissolved in the waste water. In this state, there are many well known control strategies for converting H.sub.2 S into inert compounds.
To control H.sub.2 S that is dissolved into waste water, various chemicals are fed into the waste water that convert H.sub.2 S into non-toxic and non-destructive compounds. These chemicals are fed into the waste water based upon the volume of water to be treated. However, H.sub.2 S may or may not be present in the waste water at all times or in consistent concentrations. This results in too little or too much destructor chemical being injected into the waste water the majority of the time. When too little destructor chemical is fed, only a portion of the H.sub.2 S will be destroyed. When too much destructor chemical is fed, the user is paying for chemicals that are being wasted. Once injected, most destructor chemicals are active for approximately 15 minutes or until consumed, whichever comes first.
Those concerned with these and other problems recognize the need for an improved hydrogen sulfide analyzer.